1. Field of the Invention
The present invention relates to a method of selecting a misfire of an ignition system for a multi-cylinder internal combustion engine and a device for carrying out the same.
2. Description of the Prior Art
An ignition system of the type having a distributor is shown in FIG. 10. The distributor type ignition system includes an ignition coil 901, a battery 903 and a power transistor 904 both connected to a primary winding 902 of the ignition coil 901, an engine control unit (ECU) 905 for supplying an ignition signal to the power transistor 904, a distributor 907 for distribution of a high voltage induced in a secondary winding 906, and spark plugs 908.about.911 connected to side electrodes of the distributor 907.
A single-ended distributorless ignition system shown in FIG. 11 is also known and used with a view to reducing the radio noise interference and increasing the reliability. The ignition system shown in FIG. 11 is of the type for use in a two-cylinder engine and consists of radio coils 920 and 921, power transistors 924 and 925 for intermittently allowing battery current to flow to primary windings 922 and 923 of the ignition coils 920 and 921, an engine control unit (ECU) 926 for sending an ignition signal to the power transistors 924 and 925 and spark plugs 927 and 928.
In the distributor type ignition system shown in FIG. 10, it has heretofore been practiced to install thereon a misfire detecting device which consists of a voltage dividing circuit made up of coupling condensers 914, 915, 916 and 917 of a small capacity, a condenser 918 of a relatively large capacity and a resistor 919, and a misfire detecting circuit 913, and detects a misfire of the spark plug at each cylinder on the basis of the attenuation characteristic of the divided voltage.
In the single-ended distributorless ignition system shown in FIG. 11, it has heretofore been practiced to install thereon a misfire detecting device which consists of a voltage divider made up of coupling condensers 929 and 930 of a small capacity, a condenser 931 of a relatively large capacity and a resistor 932, and a misfire detecting circuit 933, and detects a misfire of the spark plug at each cylinder on the basis of the attenuation characteristic of the divided voltage.
The misfire detecting device for installation on the distributor type ignition system requires the coupling condensers 914, 915, 916 and 917 of the small capacity, of the same number as the cylinders and a fixing device for fixing the condensers to high-tension codes, thus increasing the cost. The misfire detecting device for installation on the distributorless ignition system also requires the coupling condensers 929 and 930 of the small capacity, of the same number as the cylinders.